The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.
Reamers for enlarging boreholes drilled for oil wells and mine shafts have been known in the drilling art for many decades. Typically, a reamer includes a central body having three or more roller reamer units mounted at circumferentially spaced intervals around the tool body. The reamer tool is mounted in a string of drill pipe (drill collars) or other rotatable pipe such that the reamer is rotated with the drill pipe through the well bore in order to enlarge the bore. The roller reamer units rollably engage the well bore wall to enlarge the bore as the drill string moves through the hole. Roller reamers are used to roll against the borehole wall of an in-gauge borehole to reduce the torque of the drill collars against the borehole wall of a directionally drilled hole. An example of a roller reamer tool is found in U.S. Pat. No. 3,977,481 of Fisk which discloses three roller reamer units mounted on a tool body. Each roller unit includes a centrally mounted shaft having the roller mounted onto the bearing shaft for rotation therewith. The bearing shaft and roller mount upper and lower thrust bearings and seal rings to seal off an internal region between the bearing shaft and the roller. This internal region is lubricated utilizing a pressure balancing internal piston to maintain lubrication in spite of variations in pressure surrounding the tool. Protecting the roller reamer lubricant, e.g., grease, from pollution from the borehole environment and managing the increased pressure of a roller reamer lubricant pressure due to heat generated by operational friction are both long-felt needs in the art.
Another example of such a roller reamer is found in U.S. Pat. No. 4,182,425 of Garrett which discloses in several embodiments roller reamers having a variety of features. These roller reamers are mounted in position on cylindrical bearing blocks which fit in cylindrical recesses in the tool body. The roller reamers include rollers or cutters which are mounted onto a stationary shaft and are held against thrust by a series of ball bearings or, in a different embodiment, by a thrust flange. Additionally, a lubricant is sealed in between the stationary shaft and the rollers. The lubricant may be held in the region between the stationary shaft and the rotating roller or cutter by means of a flexible diaphragm which acts to equalize the pressure within the lubricating region.
Roller assemblies of roller reamers are generally intended to be coupled with a reamer body, or tool body, yet freely rotate about an axis of a dedicated shaft that is parallel with a central axis of the tool body. One problem with roller reamers is that under the conditions commonly encountered during drilling, rock chips and other debris can build up proximate to one or more roller assemblies, which may jam or slow rotation of the roller assemblies, thereby reducing their effectiveness. Also, even under normal operating conditions, rotation of the roller assemblies can also cause a roller assembly to increase in temperature which further increases the stress on the rotating parts and the pressure of the contained lubricant. Increased stress may cause those rotating parts to wear more quickly. This is a costly problem because the reamer will have to be brought to the surface, dismantled and reassembled.
The prior art teaches that lubricant may be supplied interstitially between a roller assembly and a shaft about which the roller assembly is positioned. It is vital to the operation of the roller reamer that the lubricant and the roller assemblies avoid pollution of the roller lubricant under high temperatures and pressures. Yet the prior art fails to optimally address the needs of roller reamers to provide adequate volumes of unpolluted lubricant between the bearing shaft and the roller assembly for prolonged periods and to reduce the frequency of required above-ground maintenance on the reamer assembly and the comprising reamer. The prior art also fails optimally compensate for the increase in pressure experienced by the reamer lubricant in high temperature operations.
It is an object of the present invention to provide a useful alternative means to both impede pollution of lubricant within a roller reamer during use in a downhole environment and to permit lubricant to escape from containment within a roller reamer at preselected lubricant pressures.